Various spin coating apparatuses that apply thin films using coating solutions such as photoresist to rotating substrates such as wafers, are well known. A coating solution is spread over the wafer by centrifugal force to form a thin film. During the coating process, a solution, for example a photoresist solution comprising a solvent and a photoresist resin, is deposited on the central portion of the substrate and is dispersed from the central substrate portion to a peripheral substrate portion as the substrate is rotated on the spin chuck, thereby forming a thin film over the substrate. When a substrate is non circular, such as a rectangular substrate, a layer of photoresist having thicker corners or “fringes” tends to form. This is thought to be formed by a turbulent air flow adjacent to the spinning substrate. Air contacting the top surface of the rotating substrate is driven to form a nonturbulent air flow caused by the substrate and the air which contacts it. This nonturbulent air flow moves in the same direction as the rotating substrate. However, the side surface of the spinning substrate causes another air flow that is turbulent when the substrate is noncircular. When the substrate is circular, the air flow is parallel to the side wall and does not typically interfere with the air flow of the top surface. When the substrate is non circular, for example rectangular, the side walls cause air flows of different directions and speeds generating the turbulent flow disturbing the top nonturbulent air flow resulting in “fringes” at the corners of the substrate.
Also, during dispersion of the photoresist solution from the central portion to the peripheral portion of a square or large round rotating substrate, the solvent in the resist tends to evaporate quicker towards the ends of the substrate resulting in a varying thickness of the photoresist layer.
It is desired to provide a uniform thickness of a material applied by spin coating. The following are examples of spin coating apparatuses devised to provide a uniform thickness of a coating film. U.S. Pat. No. 5,069,156 to Suzuki discloses a spin coating apparatus including a rotatable support for a non circular substrate that is coaxially fixed to an annular member having an inward overhanging inward wall. The annular member assists in suppressing undesirable aerodynamic forces exerted on a photoresist film by turbulent air flow that occurs during rotation of the substrate.
U.S. Pat. No. 6,576,055 to Shirley discloses an apparatus for forming a uniform liquid layer on a substrate. In one embodiment, the apparatus includes a support that engages less than the entire surface of the substrate and a barrier that can extend over the upper surface of the substrate and rotate at the same rate of the substrate to separate a rotating air mass within the barrier from a stationary air mass external to the barrier. A prior art apparatus is also disclosed that has a cover releasably placed on the chuck to rotate with the chuck and substrate. The cover includes an aperture that allows fluid to pass from the fluid supply to the substrate.
U.S. Pat. No. 5,688,322 to Motoda et al. discloses an apparatus for coating resist comprising a spin-chuck capable of rotating and holding a substrate and a rotating cup surrounding the held substrate and rotated in synchronism with the spin chuck. A cover is provided over the rotating cup and in a center bottom portion of the rotating cup an opening portion is formed. At the peripheral edge of the opening portion the upper peripheral edge of a rotating collar is connected. The rotating collar is connected to a driving pulley driven by a spin motor. The spin chuck and rotating chuck are rotated in a synchronized manner. Between the upper surface of the bottom portion of the rotating cup and the lower surface of the spin chuck, a sealing mechanism is provided.
U.S. Pat. No. 5,234,499 to Sasaki et al. discloses a spin coating apparatus including a rotary table having a boss under its central surface fitting over a rotary shaft. The rotary table carriers a spacer ring and a ring plate connecting an upper rotary plate to the rotary table. An upper support plate is detachably attached to the ring plate by knob bolts and is bolted to the upper rotary plate beneath it. The rotary table and upper rotary plate form a substrate treating space with peripheral openings allowing a part of the coating solution to scatter outwardly therefrom.
U.S. Pat. No. 5,656,082 to Takatsuki et al. discloses a liquid applying apparatus that includes a rotary member having a table for supporting a substrate and a cover movable above the table and operable to define a closed space in combination with the disk table. A sealing arrangement including a sealing ring and a ring accommodation groove is provided between the disk table and the cover member to seal the closed space.
U.S. Patent Application Publication No. 2001/000395 to Sada et al. discloses a coating processing apparatus with a rotating cup having an opening portion on the top thereof for housing a substrate, a spin chuck for rotating the substrate in the rotating cup, and a lid body having an opening for dispensing resist and attached to the rotating cup. The bottom surface of the rotating cup has a central opening therein through which an axial spin drive extends which is connected to the bottom surface.
Though many devices are known for providing a uniform film thickness, what is desired is a device which is easily affixed to different spin coating apparatuses.
It is an object to provide an apparatus that will minimize “fringe” formation and/or edge buildup.
It is another object to provide an apparatus that will provide a uniform or substantially uniform coating film on a substrate.